1. Field of the Invention
The invention relates to a method of producing an ozoniferous process gas in which oxygen or an oxygen-containing charge gas is enriched with ozone in one or more ozone producers, the process gas leaving the ozone producer or ozone producers and enriched with ozone. The enriched gas is fed to a compressor or a compressor group consisting of a plurality of compressors connected in parallel. Pressure is increased relative to the pressure on the suction side of the compressor, and is then fed to a reactor or another consumer, the process-gas delivery flow being adjustable and/or controllable.
U.S. Pat. No. 5,366,703 for example, discloses a method of this generic category.
2. Discussion of Background
In industrial applications, in the compression of gases to predeterminable final pressures, the delivery flow must also always be controlled, in which case, especially in processing applications where chemicals have to interact with one another, the mass flow and not the volumetric flow will be the variable to be controlled. Depending on compressor type and in particular depending on volumetrically acting compressor type (delivered volumetric flow is approximately constant and independent of the density). In the case of reciprocating pressure-piston, gear, screw compressors, rotating compressors and liquid ring pumps, this control may be effected according to the prior art via a speed control, a throttle control on the pressure side, intermittent operation of the compressor in combination with an accumulator or via a compressor bypass control.
If the gas flow to be compressed in such a processing application is an ozoniferous gas, such as for the bleaching of pulp by means of ozone for example, or in circuits having as high an ozone absorption in water as possible, apart from the requirement for controllability of the mass delivery flow there is also the requirement to prevent as far as possible the destruction of the ozone in the compressor, e.g. as a result of temperature rise during compression.
For the compression of ozoniferous gas, these requirements can best be fulfilled with water ring pumps, although the suitability of water-cooled single screw compressors is also mentioned in the technical literature. The compression of such ozoniferous gases by means of injectors is also possible, but is restricted to applications having a smaller pressure increase. In the case of the water ring pump mainly used (cf., e.g., LUEGGER volume 6 "Lexikon der Energietechnik und Kraftmaachinen", Deutsche Verlagsanstalt Stuttgart 1967, page 387, keyword "Flussigkeitsring-Verdichter"), delivery-flow control via adaptation of the vane rotor speed can be used only to a very limited extent on account of the requisite stability of the water ring formed, and an intermittent operation or variable throttling on the pressure side are ruled out for reasons of economy and because of the higher pressure-increase rates desired. Up to now such water ring pumps for the applications mentioned have been controlled for mass delivery flow by means of a combination of suction-flow control member and compressor bypass control (circulation control). In this case, the compressor is always operated with the same power input and the same gas flow, and the differential flow between compressor gas flow and the desired gas delivery flow is expanded to suction pressure via a bypass control valve and fed to the compressor again. Here, the control variable for the bypass is the adjustable (but otherwise kept constant) suction pressure of the compressor. At positive compression pressures of 10 to 14 bar for example, the delivery flow could thus be controlled within an appropriate range of about 50 to 100%, the compressor suction pressure being set just below the ozone gas pressure. The ozone-producer pressure is always higher than the atmospheric pressure and is kept constant; the positive pressure is typically between 0.4 bar and 2.0 bar, which means that the pressure upstream of the compressor is also always higher than the atmospheric pressure. This is a special mode of operation of such water ring compressors which up to now has only been used in combination with ozone production (cf. U.S. Pat. No. 5,366,703).
In applications of water ring pumps with this control concept, however, ozone decomposition has nonetheless been observed, the extent of which has turned out to be approximately proportional to the set bypass flow and which has therefore led to undesirable additional consumption of energy and charge gas, especially at lower delivery-flow part loads.